Digital cellar system including digital mobile telephone apparatuses has used to TDMA (Time Division Multiple Access) format using coded audio signal, and it is possible to be used by plural subscriber apparatuses only in one channel. Concretely, subscriber apparatus selects a channel having strongest electric field by scanning whole 124 channels at the time of reaching radio wave. And the apparatus detects a control channel allocated to each region, and receive the channel. In this system, the number of available channels per one cell is 124. A position of the control channel is not fixed to a specific channel of said 124 channels. Therefore, an apparatus of this system is scanning whole 124 channels sequentially, sorting them in order for signal strength, and searching FCCH (Frequency Control Channel) in the list sorted. Control channel searched in this manner is used for generating time slots, and transmitting many kinds of information. In this digital cellar system, it is used for transmitting information from each subscriber to a base station, communicating between adjacent base stations, and calling subscriber from a base station.
The subscriber detects signal which is inserted periodically in this control channel. And it adjusts operating timing based on this signal, and detects a coarse position of time slot of existence of necessary information.
The signal in the frequency control channel is synchronized by a bit pattern continuing zeros for predetermined number of bits in the case of being received and decoded by the digital mobile phone subscriber. And it is transmitted after GMSK (Gaussian filtered Minimum Shift Keying) modulation with differential coding.
The FIG. 1 shows a signal in the FCCH, which is complex of I and Q signal having modulated information to two sinusoidal waves which have 90 degree phase difference. The frequency of this signal is offset +67.7 kHz from a carrier frequency.
A digital mobile phone apparatus detects a timing of FCCH signal from received signal by a band pass filter, and synchronizes whole operation of this set based on detected timing.
In such case of filtering FCCH signal by a band pass filter, an accuracy of detection becomes higher corresponding to becoming narrower a bandwidth of the filter. But if bandwidth become narrow, characteristics of a time response become slow.
It becomes difficult to detect a FCCH according to becoming slow of time response characteristics, because a continuous term of the signal of FCCH of a GSM digital cellar system is only 550 .mu.s.
In the digital mobile phone apparatus, sometimes frequency deviation caused by Doppler effect is occurring, and a signal not belonged to FCCH has sometimes same frequency to FCCH. Therefore, if a band pass filter is used, sometimes a timing of a signal of FCCH is detected not correctly or is not detected at all. In this case, it takes much time to ready to communicate because an apparatus tries many times to detect FCCH which is transmitted periodically with predetermined period.
Another method of detecting FCCH is detecting from decoded data stream. An FCCH is being able to detect by a correlation detecting utilizing continuity of decoded data stream or a pattern matching comparing predetermined pattern. But even in this method, much error is occurred because of Doppler deviation, noise, or fading.
Specially, a noise level sometimes become worse for less than 10 dB of Eb/No. (Eb/No is a common value which expresses a state of communication medium. Eb is an energy per one bit for communication. No is a noise power density.) In this case, an error rate of decoded data stream becomes higher, and the FCCH is not detected correctly.
There is the other method for detecting the FCCH that is generating I, Q signal by an orthogonal detecting from received signal, and detecting correlation of I, Q signal utilizing a character that these signal each has an information component with 90 degrees phase difference each other. But if there are many repeating patterns in the signal not in the FCCH, it is much possibility to detect these signal as if signal of FCCH by mistake, because there is much correlation between these signal.
The purpose of this invention is to provide a radio receiver apparatus and a radio receiving method which can detect said synchronized signal of the FCCH easily and correctly.
According to the present invention, there is provided a radio receiver apparatus for decoding a received signal based on a predetermined pattern of synchronization signal which is inserted in a predetermined period, comprising:
demodulating means for demodulating the received signal to a base band signal, decoding means for decoding an output signal of said demodulating means to form a data signal; PA1 reference signal generating means for generating a reference signal based on an output signal of said decoding means; and PA1 correlation value detecting means for detecting a complex correlation value between said data signal and said reference signal; wherein PA1 said apparatus detects synchronizing signal based on said detected complex correlation value, and decodes based on said detected synchronization signal. PA1 a demodulating step for demodulating a received signal to a base band signal; PA1 a decoding step for decoding an output signal of said demodulating step to a data signal; PA1 a reference signal generating step for generating a reference signal based on an output signal of said decoding step; and PA1 a correlation value detecting step for detecting a complex correlation value between said data signal and said reference signal, wherein; PA1 the method includes steps of:
According to the present invention, there is also provided a radio receiving method for decoding a received signal based on a predetermined pattern of synchronization signal which is inserted in a predetermined period, comprising:
detecting synchronizing signal based on said detected complex correlation value; and PA2 decoding based on said detected synchronization signal.